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Thermodynamic study of the mushy zone of cobalt-based superalloys. Part 1: Case of a low carbon alloy

Elodie Conrath, Patrice Berthod

In order to better know the high temperature metallurgical state of a lowcarbon chromium-rich cobalt-based superalloy strengthened by carbides of chromiumand tantalum, as well as to test a thermodynamic modelization tool for such ranges of temperature and of alloyÂ’s chemical composition, two types of experiments were done. First an exposure of a selected alloy at high temperature was done and finished by a water-quenching allowing characterizing its high temperature microstructure. Second thermodynamic calculations were performed for comparison with the experiments. Qualitatively the agreement was rather good (the initial microstructure of the alloy and its partially molten state at 1300°C were both predicted and observed). But mismatches appear in the quantitative field, for example concerning the volume or mass fractions of liquid at the temperature of test. However the metallurgical data obtained for the studied alloy at very high temperature by respect to its melting range, as well as the transformations of themicrostructure during quenching, are of good interest.